Broad objectives: To study the community transmission dynamics of influenza in a subtropical city state. Specific aims of this proposal: To assess the efficacy of face masks and/or hand hygiene in reducing household transmission of influenza. Summary of proposed study: Design and subjects: A cluster randomised controlled trial of 1,477 households where one resident has symptoms of influenza-like-illness (index patient). The 1,477 households will include 1,477 index patients and 4,136 'secondary contacts'. After recruitment of an index patient, a study nurse will visit the household to administer the intervention, and will revisit after 3, 6 and 9 days. We will conduct an initial pilot involving 120 households to confirm feasibility and logistics before implementation of the main study. Interventions: 1, placebo (educational talk on upper respiratory tract illness self-care); 2, placebo plus distribution of free masks and education on their use; 3, placebo plus distribution of alcohol hand rubs/dispensers and education on hand hygiene; 4, placebo plus face masks and alcohol rubs/dispensers hand hygiene interventions. Instruments: Initial assessment of influenza in an index patient will be made using the QuickVue rapid diagnostic test. Clinical influenza in secondary contacts will be assessed by self-reported symptoms. Nose and throat swabs will be collected from index patients and secondary contacts for laboratory confirmation of influenza. Main outcome measures: The proportion of secondary contacts with influenza (laboratory definition where samples are available, otherwise clinical definition) during the 10 days following randomization. Relevance: The results of this study will have important implications for influenza prevention in the community locally and globally. Moreover in light of recent fears of a new influenza pandemic, our results will inform public health policy on non-pharmaceutical interventions in a subtropical Chinese setting.